1. FIELD OF THE INVENTION:
The invention relates to a method and apparatus for selective retraction of a tubing carried perforating gun within a subterranean well.
2. DESCRIPTION OF THE PRIOR ART:
Subsequent to the drilling of a subterranean oil or gas well, a string of tubular conduit commonly referred to as "casing" is run into ,the well. Thereafter, the casing is cemented into place. After the cementing operation, it is necessary to perforate the well so that production fluids within the production zone may flow from the production zone, through holes perforated through the cement behind the casing, into holes in the casing, and through the well bore to the top of the well.
For many years the desirability of utilizing a subterranean wellbore having a non-vertical or horizontal portion traversing a production formation has been known and appreciated in the prior art. Laterally directed bores are drilled radially, usually horizontally from the primary vertical wellbore, in order to increase contact with the production formation.
Most production formations have a substantial horizontal portions and, when conventional vertical wellbores are employed to tap such production formations, a large number of vertical bores must be employed. With the drilling of a wellbore having a non-vertical or horizontal portion traversing the production formation, a much greater area of the production formation may be traversed by the wellbore and the total field of drilling costs may be substantially decreased. Additionally, after a particular horizontal wellbore has produced all of the economically available hydrocarbons, the same vertical wellbore may be re-drilled to establish another horizontal portion extending in another direction and thus prolong the utility of the vertical portion of the well and increase the productivity of the well to include the total production formation.
By use of and reference to the phrase "wellbore" herein, it is intended to include both cased and uncased wells. When uncased wells are completed, the bore hole wall defines the maximum hole diameter at a given location. When cased wells are completed, the "wall" of the well will be the internal diameter of the casing conduit.
By use of the phrase "deviated well" and "deviated wellbore", it is meant to refer to wells and wellbores which comprise a vertical entry section communicating through a relatively short radius curvature portion with a non-vertical or horizontal portion communicating with the production formation. In most instances, the production formation extends for a substantial horizontal extent and the generally linear wellbore portion traverses a substantial horizontal extent of the production formation, at least up to a distance of 1000 to 2000 feet, or more. The radius portion of the wellbore has a curvature of at least 10.degree. per 100 feet of length, and preferably a curvature lying in the range cf 10.degree. to 30.degree. per 100 feet of length.
The present invention is not limited to use in horizontal completions of deviated wells and can be used in conventional or straight hole subterranean wells. It does have particular utility in horizontal completions wherein it is desired to run into the well a perforating gun and thereafter treat or acidize a well all in one trip of the work string into and out of the well. When it is desired to perform such operations within a horizontal section of a deviated subterranean well, a completion hookup incorporating a tubing carried perforating gun in combination with the retraction apparatus of the present invention may be carried into the well on a work string carrying a retrievable packer and, somewhat below the retrievable packer, a permanent completion packer. The permanent completion packer has extending from its lowermost end a cylindrical production string having thereon a sliding sleeve mechanism for selectively opening and closing a port communicating to the annular area between the casing and the production string extending from below the permanent packer. The end of the production string is selectively sealingly latchable into a sump packer previously positioned just below the production zone. Through the interior of the production string and the permanent completion packer is carried by means of the retrievable packer a section of smaller concentrically positioned tubing having at its lowermost end the retraction apparatus of the present invention which, in turn, has affixed to its lowermost end the tubing carried perforating gun.
After activating the perforating gun, it is necessary to telescopically retract same with respect to the production string section extending from the lowermost end of the production packer so that the seal assembly surrounding the lowermost exterior of the production string may be latched into the sump packer. Thereafter, the production packer is set, the retrievable packer is unset and the apparatus is withdrawn from the well. The sliding sleeve is in the closed position, such that the production zone is thereby controllably isolated from the interior of the production string.
Of course, prior to engaging the seal assembly on the lowermost end of the production string into the sump packer any one of a number of selected treatment procedures may be effected, such as acidizing or fracturing of such zone, and such trreatment may be effected prior to setting of the permanent packer and withdrawal of the retrievable packer. Such a method and apparatus for use therein is disclosed in co-pending patent application Serial No. 345,347 filed on the same date as this application, entitled "METHOD AND APPARATUS FOR ONE TRIP HORIZONTAL COMPLETION" and assigned to the same assignee as this application.